The objectives of the proposed project are: (1) to develop biologically safe, new noninvasive methods for utilizing ultrasonic technology for determining the mechanical properties of bone, with particular reference to the state of healing at a fracture site; (2) to evaluate the use of nonmetallic devices constructed of biocompatible polymeric materials for internal fixation of bone at fracture sites. The in vitro and in vivo experimental laboratory and animal studies involved are designed to incorporate the expertise of both the clinician- investigator and the bioengineer in closely coordinated joint efforts throughout all phases of the project, a circumstance we feel is both necessary and desirable to achieve the desired objectives.